1. Field of the Invention
The present invention relates to an automatic exposure control apparatus for single lens reflex camera.
2. Description of the Prior Art
At present the automatic exposure control of single lens reflex camera generally has four different modes, i.e., program mode, aperture priority mode, shutter time priority mode and manual mode.
The program mode is a mode in which both of the taking-lens aperture and the shutter time are automatically controlled in accordance with the luminance of object and the sensitivity of film. The aperture priority mode is a mode in which the shutter time is automatically controlled in accordance with the object luminance, film sensitivity and the set value of lens aperture. In the shutter time priority mode the lens aperture is automatically controlled in accordance with the object luminance, film sensitivity and the set value of shutter time. The manual mode is a mode in which both of the aperture and the shutter time are manually set.
The program mode and the shutter time priority mode belong to the automatic aperture control mode in which the aperture value is automatically controlled. The aperture priority mode and the manual mode belong to the manual aperture control mode in which the aperture value is manually set.
On the other hand there are two different types of lenses which can be mounted on the single lens reflex camera having the above four modes. The first is such type of lens adaptable for the automatic aperture control mode. The second is that adaptable for the manual aperture control mode. Therefore, as described in U.S. Pat. No. 4,269,497, it is required for the lens to be provided with means for generating a signal informing of whether the automatic aperture control mode is possible with the lens.
However, sometimes man fails in exposure by mounting a lens adaptable only for the manual aperture control mode after setting the camera to the automatic aperture control mode. The prior art automatic exposure control apparatus can not prevent this kind of failure in exposure.